Spring: How to Use Values of Properties

I wrote the way to use values of properties, written in application.properties, in Spring.

In Spring, with annotation @Value, you can use the property values.

Sample Code

Make it available to use the AWS access key value written in properties file.

Of course you can write the code in the controller, but creating the class that has property value is smart. The following code is written in Kotlin.

## AWS S3
my.s3.bucket_name=bucket-name
my.s3.access_key=ABCDEFGHIJKLMN
my.s3.access_secret=THIS/IS/ACCESS/SECRET

## AWS S3

my.s3.bucket_name=bucket-name

my.s3.access_key=ABCDEFGHIJKLMN

my.s3.access_secret=THIS/IS/ACCESS/SECRET

package com.example.sample.config
import com.amazonaws.auth.AWSCredentials
import com.amazonaws.auth.BasicAWSCredentials
import org.springframework.beans.factory.annotation.Value
import org.springframework.stereotype.Component
@Configuration
open class AwsConfig {
@Value("${my.s3.bucket_name}")
lateinit var bucketName: String
@Value("${my.s3.access_key}")
lateinit var accessKey: String
@Value("${my.s3.access_secret}")
lateinit var accessSecret: String
val credentials: AWSCredentials
get() = BasicAWSCredentials(accessKey, accessSecret)
}

package com.example.sample.config

import com.amazonaws.auth.AWSCredentials

import com.amazonaws.auth.BasicAWSCredentials

import org.springframework.beans.factory.annotation.Value

import org.springframework.stereotype.Component

@Configuration

open class AwsConfig {

@Value("${my.s3.bucket_name}")

lateinit var bucketName: String

@Value("${my.s3.access_key}")

lateinit var accessKey: String

@Value("${my.s3.access_secret}")

lateinit var accessSecret: String

val credentials: AWSCredentials

get() = BasicAWSCredentials(accessKey, accessSecret)

}

Pass the @Value annotation, the key value in properties. When I create my own key and value in properties file, I start the key name with “my” to differentiate it from conflicting with one already used in libraries, in most case.

This scheme can be useful when you should use value according to the system environment, like production or development.

Above AwsConfig class has @Configuration annotation. @Component annotation works in the same way.

How to Use Config Class

Then, here’s a sample code using AwsConfig above.

@Component
open class AwsS3Gateway {
@Autowired
lateinit var awsConfig: AwsConfig
var s3ClientCache: AmazonS3Client? = null
private fun getS3Client(): AmazonS3Client {
// ToDo; S3Client Session Management
if (s3ClientCache == null)
s3ClientCache = generateS3Client()
return s3ClientCache!!
}
private fun generateS3Client(): AmazonS3Client {
return AmazonS3Client(awsConfig.credentials)
}
// ...
}

@Component

open class AwsS3Gateway {

@Autowired

lateinit var awsConfig: AwsConfig

var s3ClientCache: AmazonS3Client? = null

private fun getS3Client(): AmazonS3Client {

// ToDo; S3Client Session Management

if (s3ClientCache == null)

s3ClientCache = generateS3Client()

return s3ClientCache!!

}

private fun generateS3Client(): AmazonS3Client {

return AmazonS3Client(awsConfig.credentials)

}

// ...

}

Owing to @Autowired annotation, Spring assigns awsConfig Configration class instance automatically.

The Life

Spring: How to Use Values of Properties

Sample Code

How to Use Config Class

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